1. Field of Invention
The present invention relates to an image input apparatus that reads the images of the transmitted copies of photographic film and converts them into digital data.
2. Description of Related Art
By converting film images photographed by a camera into electronic data, it becomes possible to perform more easily various types of image processing.
A film scanner is one image input apparatus for converting these film images into electronic data (Japanese Laid-Open Patent No. 5-75922).
FIG. 8 is a structural drawing showing the composition of this film scanner.
The film scanner 81 shown in FIG. 8 is constituted by a film feeding reel 83, a film loader 84, a take-up reel 85, an imaging optical system 86, a two-dimensional image sensor 87, an image signal processing circuit 88, and a video monitor 89.
Also, the imaging optical system 86 is constituted by an illuminating unit 86a and an imaging lens unit 86b.
The photographic film 82 is loaded in the film loader 84. The film feeding reel 83 feeds the photographic film 82. Also, this feed photographic film 82 is taken up by the take-up reel 85. The part from the film feeding reel 83 to the take-up reel 85 constitutes the film feeding system.
When a film cartridge 83 is loaded into the image input apparatus, an axial fork shaft 83a is driven to rotate by a fork shaft driver (not shown) automatically for a specified time, and at the same time the film 82 is delivered out from the film cartridge 83. The leader of the film delivered out is taken up tightly to take-up reel 85 (henceforth called thrust action).
When the thrust action is completed, the film 82 is wound up by causing the take-up reel 85 to rotate.
A difference is provided between the rotation speed of the fork shaft driver and the rotation speed of the take-up reel 85. That is, the take-up reel 85 rotates faster than the fork shaft driver. However, the fork shaft driver is provided with a one-way clutch. Therefore, if the rotation speed of the take-up reel 85 is faster than the fork shaft driver, the fork shaft driver slips. Consequently, there is no slacking or tearing off of the film.
For such an image input apparatus of the prior art, the thrust action was performed by delivering out the film for a specified time when the film is loaded for image reading.
In fact, commonly, the sliding resistance and friction load of the film in film cartridges are individually different for each film cartridge. Therefore, when the sliding resistance and friction load are high, there is a problem that the thrust action gets stopped automatically when the specified time has passed, regardless of the fact that the film has not all been delivered out from the film cartridge.
On the other hand, when the sliding resistance and friction load are low, the film is delivered out too much from the film feeding reel 83. Also, it is taken up on the take-up reel 85 as far as the image part of the film. As a result, there is a problem that the image on the leading frame of the film becomes unreadable.
Also, the two-dimensional image sensor 87 comprises a CCD image sensor. The image signal processing circuit 88 processes the image signals read by the two-dimensional image sensor 87. Video monitor 89 displays the images processed by the image signal processing circuit 88.
In the composition as described above, one frame of the photographic film 82 is placed in a specified position relative to the imaging optical system 86 by the actuation of the take-up reel 85. In this state, the transmitted image of the photographic film 82 illuminated by the illuminating unit 86a is read by the two-dimensional image sensor 87.
The two-dimensional image sensor 87 is for reading the images two-dimensionally. Imaging lens unit 86b performs image reading by projecting the transmitted images of the photographic film 82 onto the light-receiving area of the two-dimensional image sensor 87.
These transmitted images, are read by image sensor 87, are processed by the image signal processing circuit 88 and then displayed on the video monitor 89.
The image reading is performed at a high speed when performing such image reading, and when confirming the entire contents of a plurality of image data recorded on the photographic film. In such case, it is not necessary to read the images at high resolution, and high-speed image reading can be performed by dropping the reading resolution.
With conventional apparatus the highest resolution of the read images that can be obtained is determined based on the number of pixels of the two-dimensional image sensor. When trying to increase this resolution, it is necessary to use a two-dimensional image sensor having a higher number of pixels. Such two-dimensional image sensors of high pixel count are extremely expensive, and they end up increasing the cost of the film scanner.